1. Field of the Invention
The present invention relates to a current-steering D/A converter.
2. Related Art
A current-steering D/A converter is known (refer to JP-A Kokai No. 2004-80238). By providing a plurality of D/A converters of this kind, it is possible to perform parallel D/A conversion of a plurality of channels in parallel.
However, when a plurality of D/A converters are provided, offset errors between each operational amplifier in the D/A converters occur, or accuracy of current mirror circuits used in the D/A converters fluctuates. Due to the offset errors and the fluctuation of the current mirror accuracy, output currents of the D/A converters fluctuate as well. These may cause gain errors between the D/A converters.
To solve this kind of problem, it is supposed to share an operational amplifier or a reference-current generating part in each D/A converter. However, even if a partial circuit in the D/A converter is shared, it is not easy to equalize the current mirror accuracy of the D/A converters, and therefore the gain errors may occur in each D/A converter.
Further, when a bias voltage and a power supply voltage of a current mirror circuit in each D/A converter are shared, fluctuations of these voltages may be reduced. However, a digital noise generated by one D/A converter may be overlapped to the shared bias voltage and the power supply voltage. In this case, noises appear not only in its own output but also in an output of the other D/A converter. Such noises are generally called a crosstalk noise.
An aforementioned conventional document describes a D/A converter which can correct a gain error described above. In the D/A converter, an output voltage is compared to a desired reference voltage and gain adjustment is made until the output voltage has approached the reference voltage, thereby attaining reduction in a gain error.
However, when the output voltage is compared with a reference voltage by voltage signal processing, a circuit for performing comparison processing is complicated, which causes a problem of increasing a circuit area and part cost.